Content-addressable Storage - CAS and FCS

CAS and FCS

Content Addressable Storage (CAS) and Fixed Content Storage (FCS) are different acronyms for the same type of technology. The CAS / FCS technology is intended to store data that does not change (fixed) in time. The difference is that typically CAS exposes a digest generated by a cryptographic hash function (such as MD5 or SHA-1) from the document it refers to. If the hash function is weak, this method could be subject to collisions in an adversarial environment (different documents returning the same hash). The main advantages of CAS / FCS technology is that the location of the actual data and the number of copies is unknown to the user. The metaphor of a CAS / FCS is not that of memory and memory locations. The proper metaphor is that of a coat check. The difference is that, with a coat check, once the item has been retrieved it cannot be retrieved again. With CAS / FCS technology a client is able to retrieve the same data using the same claim check over and over.